Image scanners are widely used for scanning images of documents, photographs or films. The scanned images can be converted into electronic files, which are then stored, processed or spread. With increasing development of scanning technologies, the image scanners have experienced great growth and are now rapidly gaining in popularity.
In the early stage, the image scanner can scan one side of the document. For scanning both sides of the document, after one side of the document has been scanned, the document should be manually turned over so as to scan the other side of the document. However, the process of manually turning over the document is troublesome. Recently, a duplex scanning apparatus has been developed for automatically performing a duplex scanning operation to scan both sides of the document.
A typical duplex scanning apparatus usually comprises a flatbed image scanning portion and an automatic document feeder arranged above the flatbed image scanning portion. The flatbed image scanner portion is utilized to scan most documents regardless of a single sheet or a thick book. In a case that the thick book is scanned, the automatic document feeder is not feasible. For performing the duplex scanning operation, a stack of paper sheets are successively and continuously fed by the automatic document feeder to be transported through a scan region in the flatbed image scanning portion. For most duplex scanning apparatuses, the flatbed image scanning portion has one scanning module responsible for scanning both sides of the document. After scanned, the paper sheets are exited to the ejecting tray.
The duplex scanning operation performed by the duplex scanning apparatus having one scanning module is also referred as a three-pass scanning operation. When the document is transported across the scan region for the first time, the scanning module scans a first side of the document. When the document is transported across the scan region for the second time, the scanning module scans a second side of the document. Finally, the document is transported across the scan region for the third time to rearrange each document into the same order as that of the original stack but the scanning module does not scan the document.
Referring to FIG. 1, a schematic cross-sectional view of a conventional duplex scanning apparatus having a single scanning module is illustrated. The process of performing the duplex scanning operation by the duplex scanning apparatus 100 of FIG. 1 will be illustrated as follows. First of all, a document 111 to be scanned is placed on a sheet input tray 102, in which a first side of the document 111 faces upwardly. The automatic document feeder 113 transports the document 111 into a first passageway 104. Then, the document 111 enters a scan region 107 through a second passageway 106. When the document is transported across the scan region 107, a scanning module 105 scans the first side of the document 111. Then, the document 111 is transported across a third passageway 108 and a guiding rod 109 to an inverting region 112. The guiding rod 109 is switched to a first position leading the document 111 to the inverting region 112. Next, the document 111 in the inverting region 112 is transported to a fourth passageway 110 through the guiding rod 109, and then transported to the scan region 107 through the second passageway 106. When the document 111 is transported across the scan region 107, the scanning module 105 scans a second side of the document 111. Then, the document 111 is transported across the third passageway 108 and the guiding rod 109 to the inverting region 112. Next, the document 111 in the inverting region 112 is transported across the guiding rod 109 to the fourth passageway 110, the second passageway 106, the scan region 107 and third passageway 108. When the document passes through the scan region 107 for the third time, the scanning module 105 does not scan the document 111. Finally, the guiding rod 109 is switched to the second position, thereby leading the document 111 to the ejecting tray 103.
As previously described, the top document from a stack of documents is transported across the scan region for two times to scan the first and second sides thereof, and is then transported across the scan region for the third time to rearrange each document into the same order as that of the original stack. Since the document is transported across the scan region for three times, such a three-pass scanning operation is time-consuming and has reduced working speed.
For overcoming the above problems, another duplex scanning apparatus having two scanning modules is developed. The duplex scanning operation performed by the duplex scanning apparatus having two scanning modules is also referred as a one-pass scanning operation. When the document is transported across the scan region, the two scanning modules simultaneously scan the first and second sides of the document. In other words, the document needs to pass through the scan region for only one time to perform the duplex scanning operation. In comparison with the duplex scanning apparatus having one scanning module, the second type of duplex scanning apparatus has an increased scanning speed. However, the duplex scanning apparatus having two scanning modules is costly.
Therefore, there is a need of providing an improved duplex scanning apparatus with cost-effectiveness and enhanced working speed.